Recently, Friedrich Ostertag posted:

Neil Gould wrote:
Recently, Friedrich Ostertag
posted:

Karl-Heinz Kuenzel wrote:
Hi.

Here in Germany we had an accident with a brand new DA 42 in Speyer
(EDRY) on 3-4-07 during take off.

It seems, that the battery was down and both engine were started
with remote power.
After take off when retracting the gear, the props feathered and
both engines stopped.

You can read about that accident in German (sorry) in
www.pilotundflugzeug.de

First hearing about that accident and the background, I could not
believe it.

I don't even know where to start. How can an aircraft, that depends
on electrical power for the operation of it's engines, be airworthy
without fully redundant electrical systems? While in this particular
case the pilot might have noticed the problem, had he meticuously
follow procedures and started the second engine at the plane's own
power, it is quite easy to find failure modes that would go
unnoticed inflight, yet cause double engine failure at the instant
the gear is lowered on final. Lead batteries are known to
occasionally go flat suddenly, once the buildup of oxide makes
contact between the lead elements. Happened to me in the car once.
The engine (a diesel with mechanical injection pump) ran happily
without me even noticing the failure until I shut it down. When I
turned the power back on again, not even the lights in the
dashboard would light up, it was completely and utterly dead.

I would never have thought that they cut corners like that at
Diamond. I Hope this will not create a lot of mistrust in
aerodiesels, as it is not a diesel issue. I guess you could call it
a FADEC issue if you wanted, however it really is an issue of
redundancy of essential systems, and easily solveable as such.

I have a somewhat different take on this event. It appears to me that
the pilot didn't sufficiently understand his aircraft or the
implications of the symptoms he observed. Knowing that there was
insufficient power to start the engines, that the engine & prop
controls were dependent on electric power and that the landing gear
used an electric motor would have stopped me from taking off until
the battery/electrical system problem was addressed.

Well said, and I wouldn't disagree. However, the very same potentially
deadly failure could occur anytime the battery fails inflight, with
no way for the pilot to know about it before he actually hits the
button to lower the gear. That alone appears to me to be a major
design flaw that would make me pretty uncomfortable, batteries are
known to fail suddenly sometimes. I really would expect redundancy in
something as critical as the power supply for the fadec to be a
requirement for airworthyness. Why have two sets of magnetos on the
typical SI-engine? It's just an electrical system, too... Why have a
twin engined aircraft?

I agree that a failure mode allowing in-flight engine shutdown due to low
battery voltage implies that there may be an aspect of the design that
needs attention. On the other hand, the dead battery could have been a
symptom of a larger problem, and the existing design really is quite
reasonable.

I don't find it
surprising that the props feathered in this situation, and would even
say that it would be the expected behavior, rather than a fluke of
some kind.

If you are saying that a shut-down is to be expected when the power
supply on a fadec controlled engine fails, you are right. No modern
engine will continue running without electrical power. Even on a
diesel with common rail fuel supply (as the thielert is) without
electricity no fuel injection is possible.

Right, however, the alternator should be able to supply the electricity
needed to keep the engines running. It wouldn't surprise me to find that
the a breaker had popped when the landing gear was retracted and the pilot
didn't think to reset it.

Neil